The present invention relates to a plate mounting apparatus for causing a plate lockup apparatus to grip a printing plate (to be referred to as a plate hereinafter) held in the printing press near the circumferential surface of a plate cylinder in a printing press so as to mount the plate on the plate cylinder.
A gap having almost a rectangular section and a length almost equal to the overall length of a plate cylinder is formed in the circumferential surface of the plate cylinder for each of a variety of printing presses. A plate lockup apparatus consisting of a leading-side lockup device for fixing the leading end of a plate and a trailing-side lockup device for fixing the trailing end of the plate, fixed by the leading-side lockup device and then wound around the circumferential surface of the plate cylinder, is axially fixed on the bottom surface of the gap.
Each of the conventional leading- and trailing-side lockup devices comprises an elongated lockup table extending in the axial direction of the plate cylinder, a plurality of gripper plates, swingably supported at an edge portion of this lockup table, for gripping or releasing the plate with or from the lockup table by being opened or closed as they swing, and a plurality of cams which can be respectively engaged with gaps at the edges of the gripper plates. The plurality of cams are aligned along a pivotal cam shaft. A plurality of compression coil springs are interposed between the lockup table and the gripper plates to bias the gripper plates in an open direction.
With the above arrangement, in order to mount a plate on a plate cylinder, when the cam shaft is pivoted, the gripper plates which are divided in the axial direction of the plate are released from engagement with the cams and are simultaneously opened by the elastic forces of the compression coil springs. An end of the plate is inserted between the gripper plates and the corresponding lockup table. When the cam shaft is pivoted in the direction opposite to the direction described above, the gripper plates are pivoted against the elastic forces of the compression coil springs by the behavior of the cams and are closed, thereby gripping the leading end of the plate.
In an apparatus disclosed in Japanese Patent Laid-Open No. 1-127346, lockup tables and gripper plates extend along the radial direction of a plate cylinder so that trailing-side gripper surfaces which were formed in the circumferential direction of a conventional plate cylinder are formed along the radial direction of the plate cylinder. At the same time, a trailing-side end portion of the plate is bent at a right angle by a separate plate bending machine. With the above arrangement, the trailing-side end portion of the plate wound around the circumferential surface of the plate cylinder and having the leading-side end portion gripped by the leading-side lockup device is gripped such that the bent portion is inserted between the lockup table and the gripper plates of the trailing-side lockup device and is gripped while the gripper plates are swung by a cam mechanism. The trailing-side lockup device as a whole is then moved in the circumferential direction, and the plate is uniformly kept taut while being kept in contact with the circumferential surface of the plate cylinder.
In the plate mounting apparatus described above, however, it is difficult to insert the leading-side end portion of a plate into a narrow opening of the leading-side lockup device. This operation is time-consuming and requires much labor. In addition, since the plate guided to the trailing-side lockup device while being wound around the plate cylinder is not brought into tight contact with the circumferential surface of the plate cylinder, it is difficult to insert the almost right-angled trailing-side end portion of the plate into the opening of the trailing-side lockup device, thus prolonging time and increasing labor, resulting in inconvenience.
A conventional semi-automatic plate mounting apparatus is proposed. This apparatus includes a holding apparatus for holding a plate in a space between a plurality of printing units for multi-color printing, which is on the circumferential surface side of the plate cylinder. The plate is inserted into the leading-side lockup device while being held by the holding apparatus, and at the same time the plate is wound around the circumferential surface of the plate cylinder. The trailing-side end portion of the plate released from the holding apparatus is gripped by the trailing-side lockup device.
In the conventional semi-automatic plate mounting apparatus, however, U-shaped notches are formed in the leading- and trailing-side end portions of the plate, and reference pins which engage with these notches extend on the leading- and trailing-side plate devices, respectively. In order to mount a plate on the plate lockup devices, the end portions of the plate are held by hands, and the plate is inserted into the plate lockup devices. The plate lockup devices are closed while the reference pins are kept engaged with the notches, respectively. If the bottoms of the notches are separated from the reference pins upon closing of the plate lockup devices or if the bottom portions of the notches do not abut against the reference pins from the beginning, respectively, the plate mounting positions of the plate lockup devices become inaccurate. An error occurs in printing alignment, thereby degrading the quality of printed matters.